A traditional light source such as an incandescent light bulb generates light by using an electrical current to heat up metal filaments to a relatively high temperature. A three-way lamp has two filaments designed to produce different amounts of light. The three-way lamp is coupled to a three-way switch which activates the two filaments individually or together. As such, the three-way lamp is capable of producing light with three different brightness levels.
FIG. 1 shows a diagram of a conventional driving circuit 100. The driving circuit 100 includes a power source 102, a three-way switch 104, and a three-way lamp 106. The power source 102 provides a power voltage VAC between a line HOT and a line NEUTRAL. The three-way switch 104 receives the power voltage VAC and selectively conducts power to the line HOT1 and the line HOT2. The three-way lamp 106 includes a low-wattage filament F1 and a medium-wattage filament F2 coupled to the lines HOT1 and HOT2, respectively. Compared to the filament F2, the filament F1 is capable of emitting light having a lower brightness level.
The three-way switch 104 has four positions OFF, LOW, MED, and HI. When the three-way switch 104 is switched to the position OFF, neither the line HOT1 nor the line HOT2 conducts power to the lamp 106. Thus, the lamp 106 is turned off. When the three-way switch 104 is switched to the position LOW, the filament F1 is energized to produce light having a first brightness level B1. When the three-way switch 104 is switched to the position MED, the filament F2 is energized to produce light having a second brightness level B2. When the three-way switch 104 is switched to the position HI, the filaments F1 and F2 are both energized to produce light having a third brightness level B3, where B1 is less than B2, which is less than B3. In other words, one or both of the filaments F1 and F2 are activated based on operations of the three-way switch 104 to produce light having different brightness levels.
However, as the incandescent light bulb consumes energy in the form of heat, the driving circuit 100 may not be energy efficient.